1. Field of the Invention
The present invention generally relates to a shell-and-tube evaporator of a refrigerant system. More particularly, the present invention relates to a distributor that directs the flow of a two-phase refrigerant mixture entering the evaporator.
2. Description of Related Art
The primary components of a refrigeration chiller include a compressor, a condenser, an expansion device and an evaporator. Higher pressure refrigerant gas is delivered from the compressor to the condenser where the refrigerant gas is cooled and condensed to the liquid state. The condensed refrigerant passes from the condenser to and through the expansion device. Passage of the refrigerant through the expansion device causes a pressure drop therein and the further cooling thereof. As a result, the refrigerant delivered from the expansion device to the evaporator is a relatively cool, saturated two-phase mixture.
The two-phase refrigerant mixture delivered to the evaporator is brought into contact with a tube bundle disposed therein and through which a relatively warmer heat transfer medium, such as water, flows. That medium will have been warmed by heat exchange contact with the heat load which it is the purpose of the refrigeration chiller to cool. Heat exchange contact between the relatively cool refrigerant and the relatively warm heat transfer medium flowing through the tube bundle causes the refrigerant to vaporize and the heat transfer medium to be cooled. The now cooled medium is returned to the heat load to further cool the load while the heated and now vaporized refrigerant is directed out of the evaporator and is drawn into the compressor for recompression and delivery to the condenser in a continuous process.
The rate of heat transfer from the refrigerant to the chilled fluid can be maximized by wetting the evaporator's entire tube bundle with liquid refrigerant. Consequently, various evaporators and distributors have been designed for this purpose. Examples of such systems are disclosed in U.S. Pat. Nos. 2,012,183; 2,314,402; 3,240,265; 3,789,617; 5,836,382 and 6,655,173.
The '183 patent shows a pan for collecting liquid refrigerant draining from a tube bundle of a cylindrical shell evaporator. A pump draws the liquid refrigerant from the pan and sprays it back over the top of the tube bundle. The pan is said to minimize the amount of unused refrigerant that would otherwise be found below the tube bundle. The pump and overhead sprayer, however, add cost and complexity to the overall system.
The '402 patent illustrates what appears to be some sort of liquid refrigerant distributor underneath the evaporator's tube bundle. Since the distributor is fed by refrigerant “in liquid form,” as stated in the patent, it appears that such a distributor could contain a significant amount of liquid refrigerant that would be sheltered in a relatively ineffective heat transfer area below the tube bundle.
The '265 patent discloses an evaporator with a horizontal plate that helps create a vaporous refrigerant chamber underneath a partially submerged tube bundle. The plate and chamber, however, apparently are not used as a distributor of liquid refrigerant because a vertical pipe equalizes the pressure above and below the plate. Thus, there is generally little or no flow through the hole in the plate. Instead, the chamber is simply used for insulating the liquid refrigerant from the surrounding ambient air.
The '617 and '173 patents each disclose what appears to be a perforated horizontal plate that might serve as a liquid refrigerant distributor for an overhead tube bundle. Due to the orientation of the plates and their holes, it looks like the area underneath the plates can fill with liquid refrigerant, thus it appears that neither plate provides any significant reduction in liquid refrigerant.
The '382 patent shows a distributor disposed beneath the tube bundle of an evaporator. The distributor, however, displaces an inconsequential amount of liquid refrigerant, as the distributor is above the floor of the evaporator shell, so liquid refrigerant can collect in that area. Moreover, liquid refrigerant can also collect in areas along side the distributor as well as above and inside the distributor.
Consequently, a need exists for a refrigerant distributor that minimizes the amount of liquid refrigerant in an evaporator shell while evenly wetting the evaporator's entire tube bundle along the full length of the shell.